1. Field of the Invention
The present invention relates to a communication system. More particularly, it relates to a channel-system exchange system for a digital data radio-communication system including at least one main radio-communication channel system and a standby radio-communication channel system, in which the exchange system is provided at a reception side of the main radio-communication channel system and exchanges the main radio communication channel system for the standby radio-communication channel system and vice versa.
2. Description of the Related Art
In a digital data radio-communication system, a channel exchange system is provided at the reception side of each main radio-communication channel system. The channel exchange system exchanges a channel from its main radio-communication channel system to a standby radio-communication channel system when any device in the main radio-communication channel system fails. The channel exchange system also exchanges a channel from the standby radio-communication channel system to the main radio-communication channel system when the failed device is restored. The channel exchange system also exchanges a line when receiving data errors due to fading are increased and restores the exchanged channel when the errors are reduced. Due to the provision of the channel exchange system, the reliability of the digital data radio-communication system is improved.
In order to avoid loss of data during the channel exchange, a high-speed semiconductor switch has been employed in the channel exchange system. The high-speed semiconductor switch may substantially realize the high speed channel exchange without data loss during the exchange so far as the exchange of talk data or the like, because a one or two bit data loss does not substantially affect the quality of such data. However, the high speed channel exchange of the prior art, even with a high-speed switch, cannot avoid the loss of at least one bit of data due to the phase difference between the data received in the main radio-communication channel system and in the standby radio-communication channel system and/or pattern mismatch of serial data to parallel data conversions at a transmission side in the main and standby radio-communication channel systems. This lost data will be described in more detail with reference to specific examples. When data to be communicated is of the digital type used for a computer system or the like, i.e., each bit having an important value and being unable to be lost, loss of even one bit must be prevented. Accordingly, prior art digital data radio-communication systems having such high speed exchange means cannot be applied to such digital data communication systems with high reliability and high quality.